A common method of forming a multi-layered circuitized substrate involves forming sub-composites each including an individual layer of dielectric material and a layer of electrically conducting material thereon, and then forming electrical circuit patterns in the electrically conductive layer. The conducting material, typically copper, provides signal and voltage planes, as needed. The signal planes are typically in discrete wiring patterns. Voltage planes can be either ground or power planes, and are sometimes collectively referred to as power planes. If required, thru-holes are formed within this sub-composite structure by drilling or etching. This method relies on each successive step of adding additional dielectric layers and then forming circuitry thereon, until the desired number of conductive planes has been formed. Thru-holes may be formed upon completion of each of these successive steps, and it is also possible to form thru-holes through the entire thickness of the final multilayered composite. This requires precise drilling to form the holes at each step (if desired) in addition to the final hole formation step if holes extend through the entire thickness.
The teachings of the present invention are not limited to the manufacture of high speed substrates such as PCBs and the like, however, but are also applicable to the manufacture of substrates used for other purposes than high speed signal connections. Generally speaking, the teachings herein are applicable to any such substrates in which one or more conductive layers such as copper are bonded (e.g., laminated) to an adjacent dielectric layer and the resulting composite then used as the substrate, typically when combined with other dielectric and conductive layers to form a thicker, built-up structure. The invention is able to provide a final structure in which top pad to bottom pad resistance connectivity is controlled while still assuring effective conductive layer and dielectric layer adhesion.